Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.68   12.766%   $65.0434   $65.04   $65.05   $65.00  
  Purchase #2 $102.73   10.288%   $113.2989   $113.30   $113.30   $113.30  
  Purchase #3 $239.84   5.122%   $252.1246   $252.12   $252.10   $252.10  
  Purchase #4 $72.26   5.188%   $76.0088   $76.01   $76.00   $76.00  
  Purchase #5 $239.32   6.230%   $254.2296   $254.23   $254.25   $254.20  
  Purchase #6 $91.39   3.738%   $94.8062   $94.81   $94.80   $94.80  
  Purchase #7 $205.77   6.844%   $219.8529   $219.85   $219.85   $219.90  
  7 purchase totals = $1,008.99       $1,075.3644   $1,075.36   $1,075.35   $1,075.30